Shale Gas

When we talk about shale gas, we need to know what is shale gas. Simply speaking, shale gas refers to the natural gas produced from shale, sedimentary rocks of laminated structure formed by the deposition of successive layers of clay1, 2. The shale looks like the pages of a book, very thin (formed by compaction) and brittle (due to its composition of clay). Also the porosity and permeability of shale rocks are very low, which make it difficult and uneconomical to produce natural gas locked in tight, impermeable shale1. Thus, shale gas is regarded as unconventional gas resources which also include tight gas, coal-bed methane, and gas hydrates3. With the advancement of horizontal well drilling and hydraulic fracturing technologies, production of shale gas became technically and economically possible, even a hot topic in oil and gas industry, especially in United States4. Mr. Fred Julander, the president of Julander Energy, said that shale gas was the most important energy development since the discovery of oil5. Major gas shale basins exist throughout the lower-48 United States. There are at least 21 shale basins in more than 20 states6.

Fig. 1 Major US Shale Basins7

The Barnett Shale play is reportedly the most active natural gas play in the United States with as many as 182 drilling rigs at work in 20086, 8. According to the Railroad Commission of Texas’s statistic data, as of September 22, 2010, there are total of gas wells 14401 entered on RRC recrods since the discovery of Newark, East (Barnett Shale) Field on October 15, 19819. For January through July 2010, gas well gas production accumulated for 1025 Bcf, which accounts for 27% of Texas production9. Total natural gas production in North Texas’ Barnett Shale has passed a milestone level of 8 TCF10. Until January 1, 2009, as the biggest Barnett Shale producer, XTO Energy Inc.’s Well TRWD #H 2H in Tarrant County has produced 4.4 Bcf gas in 43 months11. While EOG Resources, Inc.’s Well Fowler $4H in Johnson County had a record of 8.6 MMCFGPD peak month as the biggest Barnett Shale well based on peak month daily average11. There are a total of 234 operators in the Newark, East (Barnett Shale) Field now9. In 2002, Devon Energy Production Co., L.P. Purchased Mitchell Energy & Development for $3.5 billion in cash and stock from Mr. George Mitchell, the father of the Barnett Shale, and has established itself as the leading producer from the Barnett Shale9, 12. Not only the advancement of technologies, but also the increased price and gas demand drove the development of shale gas. In another hand, the development of shale gas lower the price of natural gas13.

Now water issue has become the biggest problem despite of the economic downturn and resulting lower natural gas prices14. Hydraulic fracturing needs tremendous water to crack the formation thousands of feet under the ground, especially in the water lack area, such as Texas. For a typical horizontal well frac, it needs more than 3 million gallons water14. The potential pollution from the chemicals in the hydraulic fracturing fluids may halt the application of this technology15.